1. Technical Field
The present inventions relates to a CO2 capture system by chemical absorption that recovers CO2 from combustion exhaust gas, and in particular, to a CO2 capture system by chemical absorption that reduces energy loss of the CO2 capture system.
2. Background Art
To reduce emission of carbon dioxide (CO2) which causes global warming, technologies for removing CO2 from exhaust gas discharged from plants where fossil fuels are burnt have been being developed. One of those technologies is a CO2 capture system by chemical absorption which recovers CO2 from gas by means of an alkaline solvent.
Basic mechanism of the CO2 capture system by chemical absorption is described in, for example, Japanese Patent Laid-Open No. 2010-22986 (patent literature 1). CO2-containing exhaust gas is supplied to an absorber and comes in contact with a solvent therein, and the CO2 contained in the exhaust gas is absorbed by the solvent.
The solvent (rich solvent) that has absorbed CO2 is supplied to a regenerator and regenerated by releasing CO2. The regenerated solvent (lean solvent) is then supplied to an absorber and used again for absorbing CO2. The CO2 that has been released in the regenerator is compressed and supplied to underground storage equipment or the like.
Since the CO2 release reaction that regenerates the solvent is an endothermic reaction, it is necessary to heat up the rich solvent to be supplied to the regenerator and the inside of the regenerator to a temperature between 100° C. and 120° C.
The rich solvent is heated through the heat exchanger by the lean solvent supplied from the regenerator. Furthermore, the solvent is heated using heating vapor in a reboiler attached to the regenerator, and generated vapor is supplied to the regenerator, thereby heating the inside of the regenerator.
One of the problems for practical use of the CO2 capture system by chemical absorption is to reduce energy (recovery energy) necessary for regenerating the solvent. If recovery energy can be reduced, it is possible to effectively use more energy taken out from a combustion plant.
Techniques for that purpose include a vapor recompression (hereafter abbreviated as VR) technique described in WO 2009/091437 (patent literature 2) and a multi-effect technique. Furthermore, Japanese Patent Laid-Open No. 2008-62165 (patent literature 3) describes a method for heating a lean solvent by means of the heat generated when CO2 emitted from the regenerator is compressed by a compressor.